1. Field of the Invention
The present invention relates to catalysts for hydrogenating aromatic nitrites into aromatic amines, and a process for producing aromatic amines using such catalysts. The aromatic amines produced according to the present invention are useful as raw materials for curing agents, synthetic resins, isocyanates and the like.
2. Background Art
There have been proposed various metal catalyst systems for hydrogenating aromatic nitrites. For example, Japanese Patent Application Laid-Open No. 51-101930 discloses a process for producing benzylamines and dibenzylamines by hydrogenating benzonitriles or isophthalonitriles. This process employs a catalyst system composed of Raney nickel in pellet form, zirconium supported on diatomaceous earth in tablet form, reduced nickel co-catalyst, and platinum supported on alumina in tablet form. Further, Japanese Patent Application Laid-Open No. 62-129257 discloses a process for producing benzylamines by hydrogenating benzonitriles in the coexistence of ammonia using Raney nickel or Raney cobalt. Japanese Patent Application Laid-Open No. 5-97776 discloses, in Examples thereof, a process for producing benzylamines by hydrogenating benzonitriles using a cobalt-alumina catalyst. Japanese Patent Application Laid-Open Nos. 9-40630 and 10-204048 disclose a process for producing aromatic cyanomethylamines by hydrogenating only one of two nitrile groups of aromatic dinitrile in the presence of Raney catalyst containing nickel and/or cobalt.
These hydrogenation processes have the advantage that the aromatic amines are produced in high yield. In any of these processes, however, high boiling by-products of the hydrogenation adhere to the catalyst, thereby decreasing the yield of desired amine product. When such high boiling by-products undergo hydrogenolysis in order to reactivate the deactivated catalyst, the catalyst ruptures owing to rapid generation of methane and evaporation of liquid ammonia, which results in an increase in pressure differential in the reaction system, and extremely short lifetime of the catalyst.